1. Field of the Invention
This invention relates generally to preventing lash in a coupler assembly, such as a synchronizer or dog clutch for a dual clutch powershift transmission.
2. Description of the Prior Art
A powershift transmission is a geared mechanism having two input clutches, which alternately connect a power source, such as an engine or electric motor, and two transmission input shafts.
The transmission produces multiple gear ratios in forward drive and reverse drive though operation of gearing arranged in a dual layshaft configuration between the transmission input and its output. One input clutch transmits torque between the input and a first layshaft associated principally with even-numbered gears; the other input clutch transmits torque between the transmission input and a second layshaft associated principally with odd-numbered gears. The transmission produces gear ratio changes by alternately engaging a first input clutch and running in a current gear, disengaging the second input clutch, preparing a power path in the gearing for operation in the target gear, disengaging the first clutch, engaging the second clutch and preparing another power path in the gearing for operation in the next gear.
In a dual clutch powershift transmission that is shifted automatically, power is transmitted to alternating gears though separate input clutches, each attached to a separate input shaft. Usually, when the transmission operates in a desired gear, an adjacent gear is preselected, i.e. the gearing is prepared for operation in second gear when the transmission produces first gear, in order to reduce shift response time to second gear from first gear.
When the adjacent gear is pre-selected, however, the rotational inertia of the oncoming, but non-engaged input clutch and its associated input shaft, is coupled to the engaged input clutch and its input shaft. If a sudden disturbance is introduced to the transmission, i.e. the vehicle operator depresses the accelerator pedal quickly causing a rapid increase in throttle position, the engaged input clutch, input shaft and gear experience high torsional acceleration. The non-engaged, oncoming input clutch, input shaft and gear, which is coupled to the engaged clutch, shaft and gear, may oscillate torsionally producing cross gear lash at the connection to the engaged input clutch, input shaft and gear.
This oscillation, which occurs at a low magnitude of torque because only the inertia of the non-engaged elements is involved, may produce an undesirable noise. A need exists in the industry for a technique to preselect a drive path through the transmission without producing cross gear lash and noise.